@misc{indiciaeb81589e56e56,
  title = {A second order approximation in the Doppler equation.},
  author = {P N Wells and N D Luckman and R Skidmore},
  year = {1989},
  doi = {10.1016/0301-5629(89)90135-x},
  url = {https://pubmed.ncbi.nlm.nih.gov/2922884/},
  note = {Source identifier: 2922884}
}